Half-duplex communication is a technique used for PoC (Push-to-Talk over Cellular) using transceivers and mobile telephones as transceivers, which enables one-to-N communications. In recent years, PoC has been gradually in services by, among others, Sprint Nextel Corporation in the United States. While there are some methods to realize PoC, the basic schemes thereof are the same, including a PoC server having a session management function and a floor control function, and GLMS (Group and List Management Server) for managing a group list. In the present invention, the terms shown in Non-Patent Document 1 are used. Note that a user terminal configuring a part of the present invention shown below corresponds to a component called UE in Non-Patent Document 1.
As the PoC is a service for performing communications in real time, when group communications are to be performed, a user who cannot participate in PoC communications at that time because of being outside the communication area cannot participate in the communications. Further, as there is no means of recording communication contents, a user who was not able to participate in a session configuring a series of communications or in parts of the session has no way to acquire and confirm communication contents by, or a user who participated in the group communications has no way to confirm the communication contents later by.
In order to solve this problem, a technique having a means for recording communication contents in a PoC communication system has been reported (see Patent Document 1). Further, a technique having a means for storing communication contents such as voice messages transmitted from a transmission side when a terminal of a receiving side cannot perform communications has been reported (see Patent Document 2). Furthermore, a technique having a means for recording dialogue contents and if there is a member not participating in the session among the pre-registered members, notifying him/her of the fact that the dialogues are recorded (see Patent Document 3).
Non-Patent Document 1: Issued by Comneon, Ericsson, Motorola, Siemens, and Nokia, PoC Architecture; PoC Release 2.0
Patent Document 1: Japanese Unexamined Patent Publication 2005-234666
Patent Document 2: Japanese Unexamined Patent Publication 2006-191555
Patent Document 3: Japanese Unexamined Patent Publication 2005-278109